Electronic watch

ABSTRACT

An electronic watch having a balance wheel formed from two substantially round boards having at least a pair of flat permanent magnets mounted in facing relation on said boards. Said boards have an inertia of not more than 2,500 mg-mm2, the balance wheel formed from said boards and a hair spring having a frequency of not less than 4 Hz. A two-terminal coil is positioned in the magnetic field defined by said pair of permanent magnets coupled to a driving circuit formed from at least one PNP transistor and one NPN transistor, and a battery. The collector electrode of one of said transistors is connected to one terminal of the coil, the collector electrode of the other of said transistors being connected to the other terminal of said coil. Said driving circuit connects said coil with said battery intermittently according to the vibration of the balance wheel to supply current pulses to the coil to drive said balance wheel.

United States Patent [191 Tsuruishi Sept. 18, 1973 ELECTRONIC WATCH Primary Examiner-Richard B. Wilkinson Assistant Examiner -Edith C. Jackmon [75] Inventor. Yukl Tsuruishl, Suwa, Japan Atmmey AleX Friedman et a1. [73] Assignee: Kabushiki Kaisba Suwa Seikosha,

Tokyo, Japan I [57] ABSTRACT [22] Filed: Feb. 2, 1972 1 An electronic watch having a balance wheel formed PP N03 22,952 from two substantially round boards having at least a pair of flat permanent magnets mounted in facingrela- [30] Fmeign Application Priority Data tion on said boards. Said boards have an inertia of not Feb. l0' i971 Japan 46/5219 l 2500 the .balance. .wheel fmmed from sald boards and a hair spring having a frequency of not less than 4 B2. A two-terminal coil is positioned [52] U.S. Cl. 58/28 A, 58/107 in the magnetic field defined by said pair of permanent [51] Int. Cl. G04c 3/04, G04b 17/00 I d t d f d f t 58 Field of Search 58/23 RA 23 BA magnets mm a 58/23 TF 28 A 107 3l8/l27 129 least one PNP transistor and one NPN transistor, and a battery. The collector electrode of one of said transisx p References C tors is connected to one terminal of the coil, the collec tor 'electrodeof the other of said transistors being cona v UNITED STATES PATENTS nected to the other terminal 'of said coil. Said driving 3,596,461 8/1971 Reich 58/28 A circuit connects said coil with said battery intermit- 9/ 1969 Jaquet H 53/107 tently according to the vibration of the balance wheel 7 1/1968 lmahashi 58/23 AC X to supply current pulses tothecoil to drive-said balancewheel.

3 Claims, 6 Drawing Figures Patented Sept; 18, 1973 3,759,028

2 Sheets-Sheet 1 Patented Sept. 18, 1973 2 Sheets-Sheet 2 FIG. 6

as as 39 1 ELECTRONIC WATCH BACKGROUND OF THE INVENTION This invention relates to a highbeat electronic watch having a balance wheel as the time-keeping vibrator. In conventional electronic watches incorporating balance wheels, such balance wheels are generally provided with a pair of spaced round boards having two pairs of permanent magnets mounted in facing relation on the.

inside thereof to define a magnetic circuit. One or more coils are positioned in the space intermediate said pairs of permanent magnets so that'the currenttherein flows in a direction substantially vertical to the magnetic flux between said pairs of permanent magnets. Generally,- in such watches, two coils are used, a detecting coil and a drive coil. The detecting coil detects the moment when the magnetic fluxes of the permanent magnets interlink with the coil during the oscillating state of the balance wheel. The drive coil supplies the oscillating energy to the balance wheel by the application of drive current applied to the drive coil when the magnetic flux is interlinked with the detecting coil. Such detecting and drive coils are generally wound .coaxially and formed as a unit so that the two coils are disposed to interlink with the magnetic flux at the same time.

Electronic watches constructed as outlined above suffer from substantial defects. Thus, the energy supplied to the balance wheel by the drive coil cannot, be

increased, so that it is difficult to provide a high-beat watch. This results from the fact that the space allotted for the drive coil is limited and the diameter ofthe coil is also limited since the coil must be setso that the direction of the wire stream of the coil may be nearly vertical to the locus of the movement of the permanent magnets. Of course, it would be easy to provide a highbeat watch if substantial energy'consumptionwithin the watch were possible. Howeventhe life of the battery within such electronic watches must be at least one year in order to provide a commercially feasible watch. Furthermore, if the inertia of the balance wheel is extremely small, the kinetic energy of the balance wheel becomes small, so that the watch is incapable of maintaining the correct time. For this reason, a high-beat watch must have a balance wheel having an adequate inertia but the conventional drive circuits cannot efficiently supply a high-beat balance wheel with; the necessary energy for driving said balance wheel.

SUMMARY OF THE INVENTION Generally speaking, in accordance with the invention, an electronic watch is provided having a balance wheel formed from a pair of substantially flat round spaced boards having an inertia of not more than 2500 mg-mm and coupled to a hair spring so as to have a frequency of not less than 4H2. At least a pair of flat permanent magnets are mounted in facing relation on said spaced round boards to define a magnetic field therebetween. A two-terminal coil is positioned within said magnetic field and coupled to a driving circuit including at least one NPNtransistor and at least one PNlP transistor, the collector electrode of one of said transistors being connected to one terminal of said coil and the collector electrode of the other of said transistors being connected to the other terminal of said coil. The coil is connected with said battery intermittently according to the vibration of the balance wheel to supply current pulses to the coil and to drive the balance wheel. I t A The electronic driving circuit includes a first condenser connected between the collector and base electrodes of one of the transistors; a resistor connected between the base electrode of each of said transistors and the collector electrode of the other of said transistors; and a second condenser connected between the base and collector electrodes of the other of said transistors, the emitter electrodes of said respective transistors being connected respectively to the terminals of said battery for series connection therewith.

Accordingly, the object of this invention is to provide a highly accurate electronic watch utilizing a high-beat balance wheel, and to provide a drive circuit suitable for driving such a high-beat balance wheel.

A further object of the arrangement according to the invention is to provide a driving circuit for a high-beat balance wheel.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and drawings.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a partially sectioned side elevational view of the balance wheel and electronic elements of the electronic'watch in accordance with the invention;

FIG; Z-is a top plan view of the arrangement of FIG.

' FIG. 3 is a circuit diagram of a conventional driving circuit'for the balance wheel of an electronic watch;

FIG. 4 is a circuit diagram of a first embodiment of the driving circuit'for a balance wheel of an electronic watch in accordance with the invention; a

FIG. 5 is a graph showing the relation between the consumption energy A E and the amplitude 0,, of a balancewheel; and

FIG. 6 is a circuit vdiagram of a second embodiment of the driving circuit for balance wheels of electronic watches in accordance with the invention.-

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2, the balance wheel and electronic elements of the electronic watch according to the invention are depicted. The balance wheel consists of a pair of spaced flat round boards 1 mountedon a balance staff 3-which is connected to a hair spring 2. Flat permanent magnets are mounted in facing relation on the inner surface of. said flat round boards. Thus, permanent magnets '4a and 4c are mounted on the upper board in facing relation to permanent magnets 4b and 4d, respectively, to define a magnetic circuit. The polarity of said permanent magnets is selected so that magnetic'flux flows in the space between said pairs of facing permanent magnets. A balance mass 5 is mounted on each of said boards spaced from said permanent magnets to balance the balance wheel. A two-terminal coil 6 is mounted by means of support 7 in the space between said pairs of permanent magnets so as to cut the magnetic flux therebetween as said balance wheel oscillates. Support 7 also supports the electronic components 9 of the driving circuit for said coil, which are coupled to said coil through terminal pin 8. The structure of the balance wheel is similar to that of conventional electronic watches incorporating balance wheels, but such conventional electronic watches generally include threeor four-terminal coils defining both detecting and drive coils, as compared to the unitary two-terminal coil 6 of the electronic watch according to the invention.

A conventional drive circuit is depicted in FIG. 3, said circuit including a detecting coil 10 connected in series with condenser 11 for eliminating direct current flow in said detecting coil. Drive transistor 12 is connected with its emitter-collector path in series withresistor l6 and drive coil 15, said series connection being connected across battery 17. Resistor 16 is provided for adjusting the amplitude of the balance wheel. Resistor 13 is connected to the base of transistor 12 for providing bias to said transistor. Condenser 14 is connected between the base and collector of said transistor for preventing high frequency oscillation of the circuit. When the permanent magnets fixed on the balance wheel move across detecting coil 10, a voltage is induced in said coil and applied to the base of transistor 12 through condenser 11. When said base voltage reaches a predetermined level, transistor 12 is turned to its conductive state so that a drive current flows through drive coil 15. According to Flemings left-hand law, force is supplied to the balance wheel by the interaction of the drive current and the magnetic flux of the permanent magnet. Since two coils, both a detecting coil 10 and a drive coil 15, are required in the conventional, circuit the winding turns of drive coil 15 cannot be increased in number beyond a maximum level, and consequently, the driving efficiency of the arrangement is reduced and the current consumption thereof becomes relatively large.

Referring now to FIG. 4, a drive circuit in accordance with the invention is depicted wherein PNP transistor 18 is connected with its emitter-collector path in series with drive coil 19 and the emitter-collector path of NPN transistor 20. Coupling condenser 21 is connected between the base of transistor and the collector of transistor 18 in parallel with resistor 22, which provides bias for the base of transistor 20. A decoupling condenser 23 is connected between the base and collector of transistor 18 to prevent high frequency oscillation. Resistor 24 is connected between the base of transistor 18 and the collector of transistor 20 to provide bias to transistor 18. Battery 25 is connected across the series connection of transistors 18 and 20 and drive coil 19. A separate detecting coil is not i vided in the circuit of FIG. 4, drive coil 19 also serving as a detecting coil. For this reason, the number of wind-J ing turns of drive coil 19 can be increased, thereby. in

creasing driving efiiciency.

When the amplitude of the balance 'wheelis ma ximum 0,, the consumption energy AE of the balanc where K is a constant which is in proportion to the inertia of a balance wheel and is in inverse proportion to the quality factor Q.

The energy AP supplied by the drive coil to a balance wheel is given by:

AP AKef- CKeO I where Ke BN1; 8 is the effective magnetic flux density of the permanent magnets; N is the effective winding turns of the drive coil; and l is the effective length of the drive coil which is dependent on the diameter of the permanent magnets. A is a constant which is determined by the battery voltage, the resistance of the drive coil, the size of the balance wheel, etc. C is also a constant which is dependent on the size of the balance wheel.

A plot of equations (1) and (2) is shown in FIG. 5, in which the axis of abscissas represents the maximum amplitude 0,, of the balance wheel and the axis of ordinates represents the consumption energy AE of the balance wheel or the energy AP supplied by the drive coil. The curves 26-29 show the change of AE dependent on the parameter of the frequency (f) of the balance wheel. The curves 30 and 31 show the change of AP dependent on the parameter Ke. The balance wheel is stabilized at the point where AE is equal to AP. If the frequency (f) is lower and BN1 is small, the balance wheel is stabilized at the cross point 0 AE of the curves 26 and 30. Then, if AP remains constant and only the frequency (f) increases, the stabilized point is changed to the cross point 0 AE, of the curves 29 and 30. Furthermore, if BNI increases, the stabilized point is changed to the cross point 0 AE At this condition, the balance wheel can be driven with low energy consumption and at high frequency. AB is actually proportional to f, so BN1 must be greatly enlarged to assure a battery life of one year in a high-beat electronic watch using a balance wheel. However, to enlarge B or I is to also enlarge the inertia of the balance wheel, resulting in adverse effects.

On the other hand, the drive circuit in accordance with the invention utilizes a two-terminal coil so that the winding turns N of the drive coil can be increased and a highbeat watch having low power consumption may be produced. The drive circuit of FIG. 4 may be classified as an unstable blocking oscillator using conventional electronic terminology. Said circuit selfoscillates even if the balance wheel is stopped. For this reason, the balance wheel can readily self-start, while, when the amplitude of the balance wheel exceeds a predetermined value, the oscillation of the circuit synchronizes with the oscillation of the balance wheel. Referring to FIG. 6, a second embodiment of the drive circuit in accordance with the invention is depicted. In said circuit, battery 32 is connected across two seriesconnected paths, both of which include driving coil 37. The first of these paths includes the emitter-collector path of PNP transistor 34, drive coil 37 and the emittercollector path of NPN transistor 35. The second of these paths includes the emitter-collector path of PNP transistor 33, drivecoil 37 and the emitter-collector pathof NPN transistor36.

Resistor 40 serves as a base bias resistor for NPN transistor 35 while resistor 41 serves the same purpose for transistor 36. Similarly, resistors 38 and 39 serve as base bias resistors for transistors 33 and 34 respectively. Condenser 42 is connected in parallel with drive coil 37 for preventing high frequency oscillation of the circuit while coupling condensers 43 and 44 couple the base of transistor 35 with the collector of transistor 34 and the base of transistor 36 with the collector of transistor 33 respectively. The circuit of FIG. 6 is particularly adapted for driving the balance wheel at high oscillation since large amounts of energy are supplied to the balance wheel due to the efficiency of the circuit. The circuit can self-oscillate, so that the balance wheel can immediately self-start.

In order to assure battery life of one year, AE must be maintained below a certain value in consideration of driving efficiency. As the drive circuit according to the invention has high efficiency, the total power consumption can be less than a predetermined value even if AB is alarge value. An accurate watch in which the balance wheel is used as a time-keeping oscillator cannot be obtained unless the amplitude of oscillation of the balance wheel is at least 200. A watch having a frequency of about 4H2 would preferably have a balance wheel wherein the inertia is about 2500 mg-mm in order to provide an accurate and efficient watch. By using the driving circuit according to the invention, such a balance wheel can be driven with relatively small power consumption and an adequate amplitude of oscillation can be obtained. The provision of a watch having a frequency of at least 4H2 and having a balance wheel having an inertia of not more than 2,500 mgmm, in conjunction with the driving circuit according to the invention, will produce a very accurate electronic watch requiring relatively small amounts of energy. In preferred embodiments, inertia of the balance wheel should lie within the range of 900-2,500 mg-mm while frequency should lie within the range of 4-l0l-lz. t

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. v

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. An electronic watch comprising a balance wheel having a frequency of not less than 4H2 and including a balance staff, a pair of substantially flat round boards mounted in spaced relation on said balance staff, at least a pair of flat permanent magnets mounted in facing relation on said pair of flat round boards, said permanent magnets being of a polarity for the production of a magnetic field therebetween, and a hair spring coupled to said balance staff, said balance wheel having an inertia of not more than 2,500 mg-mm a two-terminal drive coil positioned in the magnetic field produced by said permanent magnets; a DC. voltage source; first and second PNP transistors; first and second NPN transistors; said two-terminal drive coil being connected between the respective collectors of said first PNP transistor and said first NPN transistor and further connected between the respective collectors of said second PNP transistor and said second NPN transistor; and cir cuit means including said transistors connecting said drive coil with said DC. voltage source in response to the voltage induced in said drive coil due to the oscillation of said balance wheel to supply current pulses to said drive coil for driving said balance wheel, said circuit means including a first condenser connected in parallel with said drive coil; first and second resistors respectively interconnecting the base of said first PNP transistor with the collector of said first NPN transistor and the base of said second PNP transistor with the collector of said second NPN transistor; third and fourth resistors respectively interconnecting the base of said first NPN transistor with the emitter of said second PNP transistor and the base of said second NPN transistor with the emitter of said first PNP transistor; and third and fourth condensers respectively coupling the base of said first NPN transistor with the collector of said first PNP transistor and the base of said second NPN transistor with the collector of said second PNP transistor.

2. An electronic watch as recited in claim 1, wherein the inertia of said boards is about 2,500 mg-mm and the frequency of said balance wheel is about 4Hz.

3. An electronic watch as recited in claim 1, wherein the inertia of said-boards lies within a range between 900 and 2,500 rng-mm and the frequency of said balance wheel lies within the range between 4 and l0Hz. 

1. An electronic watch comprising a balance wheel having a frequency of not less than 4Hz and including a balance staff, a pair of substantially flat round boards mounted in spaced relation on said balance staff, at least a pair of flat permanent magnets mounted in facing relation on said pair of flat round boards, said permanent magnets being of a polarity for the production of a magnetic field therebetween, and a hair spring coupled to said balance staff, said balance wheel having an inertia of not more than 2,500 mg-mm2 a two-terminal drive coil positioned in the magnetic field produced by said permanent magnets; a D.C. voltage source; first and second PNP transistors; first and second NPN transistors; said two-terminal drive coil being connected between the respective collectors of said first PNP transistor and said first NPN transistor and further connected between the respective collectors of said second PNP transistor and said second NPN transistor; and circuit means including said transistors connecting said drive coil with said D.C. voltage source in response to the voltage induced in said drive coil due to the oscillation of said balance wheel to supply current pulses to said drive coil for driving said balance wheel, said circuit means including a first condenser connected in parallel with said drive coil; first and second resistors respectively interconnecting the base of said first PNP transistor with the collector of said first NPN transistor and the base of said second PNP transistor with the collector of said second NPN transistor; third and fourth resistors respectively interconnecting the base of said first NPN transistor with the emitter of said second PNP transistor and the base of said second NPN transistor with the emitter of said first PNP transistor; and third and fourth condensers respectively coupling the base of said first NPN transistor with the collector of said first PNP transistor and the base of said second NPN transistor with the collector of said second PNP transistor.
 2. An electronic watch as recited in claim 1, wherein the inertia of said boards is about 2,500 mg-mm2 and the frequency of said balance wheel is about 4Hz.
 3. An electronic watch as recited in claim 1, wherein the inertia of said boards lies within a range between 900 and 2,500 mg-mm2 and the frequency of said balance wheel lies within the range between 4 and 10Hz. 